In most fires, the smoke is usually generated first, followed by the occurrence of flames. In some fires, burning of some substances generates the smoke only. Therefore, the smoke detection is a very important object for fire prevention and rescue. When using a smoke detecting system, a fire can be reported at its early stage so that the early fire fighting may be proceeded to reduce the casualties.
The conventional smoke detecting devices, such as a photoelectric smoke detector and an air sampling smoke detector, use the physical properties resulting from increase of the smoke particles as the basis of fire detection. The photoelectric smoke detector emits the light. The light is scattered and the brightness is changed when smoke particles exist in the air. Because the photoelectric smoke detector detects the variation of the brightness by light emitting to determine if there is a fire, the detecting range thereof is restricted. Therefore, the smoke detecting in large areas by the photoelectric smoke detector may not be effective. The air sampling smoke detector collects the air sample in the detecting area and analyzes the elements of the collected air to determine if there is a fire. To collect the air sample, the air sampling smoke detector must be equipped with a duct system for facilitating the detection. Besides, the sensors of the air sampling smoke detector are very expensive.
Accordingly, the conventional smoke detecting devices have the shortcomings as follows: 1) it is hard to detect a smoke in high and large-area buildings, such as the factories, the stadiums and the shopping malls, thereby wasting the early rescuing time; 2) the accuracy thereof is too low, thereby causing too many false alarms; and 3) a large number of sensors, ducts and controlling systems needs to be installed, thereby raising the cost.
Therefore, for improving the accuracy of the smoke detecting device and reducing the cost, the visual smoke detecting device has been recently developed, which identifies if there is any object whose features meet the fire smoke by using the original monitoring system in a building. Once the smoke detecting device determines the object as the fire smoke, an alarm will be generated. U.S. Pat. No. 6,184,792 discloses a method and apparatus for detecting early fire in a monitored area, which analyzes a brightness variation of video images by performing a Fast Fourier Transform (FFT) on the temporally varying pixel intensities, and U.S. Pat. No. 6,956,485 discloses a fire detection algorithm to analyze a frequency variation by a filter-analyzing technology. However, the accuracy of these detecting methods is not mentioned in theses patents, and other analyzing techniques, e.g. a chrominance variation analysis, are not applied in these patents.